Solar cell module and its installing module

ABSTRACT

A solar cell module  60  has a plurality of solar cells  14  having a plurality of parallel grooves  8  on the individual light-receiving surfaces thereof, each of the grooves having an electrode  5  for extracting output on the inner side face (electrode-forming inner side face) on one side in the width-wise direction thereof; and a support  10, 50  for supporting the solar cells  14  in an integrated manner so as to direct the light-receiving surfaces upward. The annual power output can be increased by adjusting the direction of arrangement of the electrode-forming inner side faces of the grooves  8  while taking the angle of inclination β of the light-receiving surface of the individual as-installed solar cells  14  relative to the horizontal plane and the latitude δ of the installation site of the solar cell module into consideration. This successfully provides the solar cell module capable of equalizing the output current from the individual solar cells in the module even when the sunlight obliquely irradiates the module.

TECHNICAL FIELD

[0001] This invention relates to a solar cell module and a method ofinstalling the solar cell module.

BACKGROUND ART

[0002] Solar cells generally have a finger-type electrode on the surfacethereof for the purpose of extracting generated power to the external.It is preferable for the electrode to have a larger width or largerthickness in view of improving the generation efficiency, since thelarger the sectional area of the electrode becomes, the more theelectrode reduces its resistivity. On the contrary, the electrodeprevents sunlight from entering the semiconductor material composing thesolar cells, and consequently lowers the generation efficiency. Theelectrode, typically formed by screen printing using an Ag paste,accounts for 8 to 12% of the total area of the light-receiving surfaceof the solar cells, and shadowing loss ascribable to this is understoodas an obstacle to efforts for improving the generation efficiency.

[0003] One known method ever developed in order to improve thegeneration efficiency through reducing the shadowing loss relates to anOECO (obliquely-evaporated contact) solar cell having a plurality ofgrooves with any section of rectangular, semicircular and triangularforms fabricated on the light-receiving surface thereof, and havingelectrodes formed on the individual inner side faces of the grooves onlyon a single side as viewed along the width-wise direction (“RenewableEnergy, Vol. 14, Nos. 1-4, 83-88 (1998), European Patent No.EP0905794A2).

[0004] Although the OECO solar cell has a great advantage in terms ofenergy conversion efficiency, the inventors found out through ourinvestigations that modularization of the OECO solar cell raises variousnew problems which could have not been encountered before, due to itsspecial design such that the electrodes are formed on the inner sidefaces of the grooves.

[0005] Because the OECO solar cell has the electrodes only on one sideface of each groove, the shadowed area will vary depending on the angleof incidence of sunlight, and thus the cell inevitably causes variationin the amount of photo-generated current. This is illustrated in FIG. 2.As seen in FIG. 2, a ratio of shadowed area for an angle of incidence ofα is given as B/(A+B+C), but that for an angle of incidence of α′ isgiven as B′/(A′+B′+C′). This indicates that smaller angle of incidenceincreases the shadowing loss.

[0006] To maximize the generation efficiency of the solar cell module,it is necessary to equalize output current obtainable from theindividual solar cells in the module, and thus it is important toequalize the conversion efficiency of the individual solar cells. TheOECO solar cell module is, however, not always successful in equalizingthe output current from the individual solar cells even if it isconfigured using solar cells having a uniform basic performance, andeven the cells are uniformly irradiated by sunlight. It is becauseseverity of the shadowing loss may differ from cell to cell and theoutput current may be non-uniform under an oblique incidence of sunlightif no special attention is paid on the direction of attachment of theindividual cells in the module.

[0007] Considering now that solar cell modules are generally installedon the roof of houses or buildings, and that the OECO solar cell haselectrodes only on a single side face of each groove and shows theshadowing loss variable depending on the angle of incidence of sunlightas described in the above, another disadvantage arises that total ofdaily or annual power output may differ depending on the direction towhich the electrode-forming surfaces are directed, and this may preventperformance of the solar cell module from being fully exhibited.

[0008] It is therefore a subject of the invention to provide a solarcell module in which output current from the individual solar cellscomposing the module are equalized even under oblique incidence ofsunlight, and a method of effectively installing thus-composed module.

DISCLOSURE OF THE INVENTION

[0009] As a solution to the aforementioned subject, the solar cellmodule of the invention comprises a plurality of solar cells having aplurality of parallel grooves on the individual light-receiving surfacesthereof, each of the grooves having an electrode for extracting outputon the inner side face (referred to as electrode-forming inner sideface, hereinafter) on one side in the width-wise direction thereof; anda support for supporting the solar cells in an integrated manner so asto direct the light-receiving surfaces upward; wherein the plurality ofsolar cells are attached to the support so that the longitudinaldirections of the grooves nearly coincide with each other, and so thatthe electrode-forming inner side faces are arranged on the same side.

[0010] Thus-configured solar cells used for the solar cell module of theinvention correspond to the aforementioned OECO solar cell. Because theplurality of solar cells are attached to the support so that thelongitudinal directions of the grooves nearly coincide with each other,and so that the electrode-forming inner side faces are arranged on thesame side, sunlight can irradiate the electrode-forming inner sidesurfaces of the individual solar cells at the same angle even underoblique incidence. This is successful in approximately equalizingshadowing loss which possibly occurs in the individual solar cells, andin equalizing the output current.

[0011] Taking convenience in fabrication of the grooves intoconsideration, each groove of the solar cell preferably has any sectionof rectangular, semicircular and triangular forms.

[0012] The invention is also to provide a method of installing the solarcell module of the invention. More specifically, the direction ofarrangement of the electrode-forming inner side faces of the grooves ofthe individual solar cells are adjusted depending on the angle ofinclination β of the light-receiving surfaces of the individualas-installed solar cells away from the horizontal plane, and on thelatitude δ of the installation site of the solar cell module.

[0013] Examinations by the inventors have revealed that the OECO solarcell, having the electrode-forming inner side face only on a single sideface of each groove, showed completely different patterns of intensityof sunlight coming into the electrode, severity of the shadowing, anddaily or annual variation thereof depending on the attitude of themodule or on the latitude of the installation site. Whereas theinvention succeeded in fully expressing performances of the solar cellmodule, and, as a consequence, in increasing the daily or annual powergeneration of the solar cell module, by defining an angle of inclinationβ of the light-receiving surfaces of the individual solar cells awayfrom the horizontal plane as the attitude of the module, and byadjusting the direction of arrangement of the electrode-forming innerside faces depending on p and the latitude δ of the installation site.

BRIEF DESCRIPTION OF DRAWINGS

[0014]FIG. 1 is a schematic view showing an exemplary sectionalstructure of an OECO solar cell;

[0015]FIG. 2 is an explanatory drawing showing relations among groovesformed on the OECO solar cell, electrodes and sunlight;

[0016]FIG. 3 is a perspective view showing an arrangement pattern of thesolar cells in a solar cell module according to the invention;

[0017]FIG. 4 is a perspective view showing a method of installing thesolar cell module according to the invention;

[0018]FIG. 5 is a perspective view showing an exemplary installation ofthe solar cell module while directing the electrode-forming inner sidefaces upward;

[0019]FIG. 6 is a perspective view showing an exemplary installation ofthe solar cell module while directing the electrode-forming inner sidefaces downward;

[0020]FIG. 7 is a schematic view showing an exemplary installation ofthe solar cell module on a roof having a south aspect;

[0021]FIG. 8 is a schematic view showing one embodiment of the solarcell module;

[0022]FIG. 9 is a flow chart of a process for deriving formulae (1) and(2);

[0023]FIG. 10 is a graph showing a relation among latitude of theinstallation site of the solar cell module, turning-point angle andorientation of the electrode-forming inner side faces;

[0024]FIG. 11 is a graph showing time-depended changes in the shadowingloss for the case where the solar cell module is situated at 30° NorthLatitude and at an angle of installation of 25°;

[0025]FIG. 12 is a graph showing time-depended changes in the shadowingloss for the case where the solar cell module is situated at 30° NorthLatitude and at an angle of installation of 30°;

[0026]FIG. 13 is a graph showing time-depended changes in the shadowingloss for the case where the solar cell module is situated at 30° NorthLatitude and at an angle of installation of 35°; FIG. 14 is a graphshowing time-depended changes in the shadowing loss for the case wherethe solar cell module is situated at 50° North Latitude and at an angleof installation of 45°;

[0027]FIG. 15 is a graph showing time-depended changes in the shadowingloss for the case where the solar cell module is situated at 50° NorthLatitude and at an angle of installation of 50°;

[0028]FIG. 16 is a graph showing time-depended changes in the shadowingloss for the case where the solar cell module is situated at 50° NorthLatitude and at an angle of installation of 55°;

[0029]FIG. 17 is a graph showing relations between the angle ofinstallation and average effective amount of received solar energy ofthe solar cell module situated at 30° North Latitude;

[0030]FIG. 18 is a graph showing relations between the angle ofinstallation and average effective amount of received solar energy ofthe solar cell module situated at 50° North Latitude;

[0031]FIG. 19 is a schematic sectional view showing dimensions of thegrooves formed on the surface of the solar cell;

[0032]FIG. 20 is a drawing for explaining orientation of the groovesaltered depending on aspect of the roof;

[0033]FIG. 21 is a schematic sectional view showing an exemplaryconstitution of the solar cell module allowing independent adjustment ofthe direction of the solar cell units;

[0034]FIG. 22 is a schematic sectional view showing an exemplary solarcell unit having a variable mechanism for angle of inclination of thelight-receiving surface;

[0035]FIG. 23 is a drawing for explaining definition of a celestialcoordinates system;

[0036]FIG. 24 is a perspective view showing relations among thelongitudinal direction of the solar cell module and the grooves of thesolar cells, positional relation with respect to the horizontal plane,and angle of installation; and

[0037]FIG. 25 is a graph showing relations among various azimuth anglesψ, latitude δ and turning-point angle β.

BEST MODES FOR CARRYING OUT THE INVENTION

[0038] The following paragraphs will describe best modes for carryingout the invention making reference to the attached drawings, where it isto be understood that the invention is by no means limited to these bestmodes for carrying out the invention. FIG. 1 is a schematic view showingan exemplary sectional structure of a solar cell used for the solar cellmodule of the invention. The solar cell 14 is configured so that a largenumber of grooves 8 of approx. several-hundred-micrometers wide andapprox. 100 μm deep are formed in parallel on a first main surface(light-receiving surface) 24 of a p-type silicon single crystalsubstrate 2 sliced out from a silicon single crystal ingot. Thesegrooves 8 can be carved en bloc using a set of hundreds to thousands ofconcentrically-jointed rotary blades which rotate all together, where itis also allowable to divide the carving operation into several numbersof the run.

[0039] On the first main surface 24 of the substrate 2 having thegrooves 8 thus formed thereon, an emitter layer 3 is formed by thermallydiffusing phosphorus as an n-type dopant, so as to produce a p-njunction portion. On the emitter layer 3, a thin silicon oxide film 4which functions as a tunnel insulating film is formed typically by thethermal oxidation process.

[0040] On the silicon oxide film 4, electrodes 5 are formed. Each of theelectrodes 5 is formed typically by depositing, in a vacuum evaporationapparatus, an electrode material (e.g., a metal such as aluminum) on aninner side face (electrode-forming inner side face) on one side of eachgroove 8, and this style of deposition is attained by inclining thesubstrate 2 relative to an evaporation source at a least necessary angleor more, so as to allow the electrode material to deposit on the innerside face predominantly on one side in the width-wise direction of eachgroove, as described later (this is where the name of OECO came from. Itis to be noted that unnecessary portion of the electrode material whichdeposit also on the top surface of projected portions 9 formed betweenevery adjacent grooves 8, 8 can be removed later by an etching solutionsuch as phosphoric acid solution). The entire surface of the first mainsurface 24 of the substrate 2, together with the electrodes 5, iscovered with a silicon nitride film 6 which serves as a protective layerand an anti-reflection film. On the other hand, the substrate 2 has,also on the back surface thereof, the silicon nitride film 6 and anelectrode 7.

[0041]FIG. 8 shows an exemplary solar cell module using theaforementioned solar cells 14. The solar cell module 60 has a support 50for supporting a plurality of solar cells 14 in an integrated manner soas to direct the light-receiving surfaces 24 upward. The plurality ofsolar cells 14 are attached to the support so that the longitudinaldirections of the grooves 8 nearly coincide with each other with respectto the bottom edge of the support 50, and so that the electrode-forminginner side faces 1, and more specifically the electrodes 5, of all solarcells 14 are arranged on the same side as shown in FIG. 3.

[0042] Direction of arrangement of the electrode-forming inner sidefaces 1 in the installation of the solar cell module 60 is adjustedtypically depending on the angle of inclination β of the light-receivingsurfaces 24 away from the horizontal plane, and on the latitude δ of theinstallation site, in order to optimize the annual power output. In thebest mode for carrying out the invention, the plurality of the solarcells 14 are attached to the support 50 (FIG. 8) so that positions ofthe electrode-forming inner side faces 1 are arbitrarily selectedbetween a first position (FIG. 5) and a second position (FIG. 6) whichare in a 180°-inverted positional relation within a plane parallel tothe light-receiving surface, for the convenience of carrying out thespecific embodiments of the installation method described later.

[0043] More specifically, the plurality of solar cells 14 arecollectively attached to a cell holding member 10, and the cell holdingmember 10 is attached to an installation base 50 as the support.Variation in the direction of attachment of the cell holding member 10to the installation base 50 results in positional changes in theelectrode-forming inner side faces 1 (FIG. 3) of the plurality of solarcells 14 collectively between the first position and the secondposition. Some troubles may, however, arise in the attachment of thesolar cells 14 to the cell holding member 10 or to the installation base50 when the orientation of the grooves 8 formed on the solar cells 14are not visually recognizable. It is therefore convenient to provide thesolar cells 14 with a direction-identifying marking (orientation notch,orientation flat, etc.) which satisfies a predetermined positionalrelation with the grooves 8.

[0044] The cell holding member 10 herein has a form of plate, and theindividual solar cells 14 are attached as being aligned with the surfacethereof. Angle of inclination β of the cell holding member 10 thusrepresents angle of inclination of the light-receiving surfaces 24. Onthe other hand, the installation base 50 has a form of frame, and thecell holding member 10 is attached thereto with the aid of a detachablejoining mechanism, which is typified herein by screw holes 52 bored inthe installation base 50 and screws penetrating the cell holding member10 and tightened into the screw holes 52. Direction of the cell holdingmember 10 can be turned by unscrewing the screws 51, turning the cellholding member 10 in the direction indicated by arrow, and re-tighteningthe screws 51.

[0045] It is also allowable to attach the plurality of solar cells 14 sothat the individual directions thereof can be adjustable in anindependent manner. FIG. 21 shows an exemplary configuration therefor.In this example, each solar cell 14 is mounted on a wiring base so as toconfigure a disk-formed solar cell unit 35, and the solar cell unit 35is attached to a cell holding portion 10 b (a spot-faced recess having acylindrical inner surface herein) formed in the cell holding member 10so as to be rotatable around the axial line. Position of theelectrode-forming inner side face 1 (FIG. 3) can thus be altered byrotating the solar cell unit 35. The cell holding portion 10 b has, onthe inner surface thereof, an elastic holding portion 10 c typicallycomposed of rubber, so as to support the attachment position of thesolar cell unit 35 placed in the cell holding portion 10 b underpressure. Output lines of the solar cell unit 35 are drawn out from athrough hole 10 a which communicates with the cell holding portion 10 b.

[0046] In most cases of installing the solar cell module 60 on a roof,it is a general practice to choose the sunny south aspect thereof as aninstallation site as shown in FIG. 7. Considering now about solar cellpower generation using the natural light, an essential point is that howeffectively the light can be converted into electric power out of thetime zone around the meridian passage abundant in light energy, butrather in the time zones before or after the meridian passage lessabundant in the light energy, that is in the morning or in the evening.The shadowing loss becomes more likely to occur when the light isirradiated so that the orthogonal projection thereof on thelight-receiving surface crosses the longitudinal direction of thegrooves 8, so that it is not desirable for the solar cell to remain insuch situation for a long duration in the morning and evening in view ofraising the generation efficiency. For an exemplary case where the solarcell module 60 is installed on a roof having northward and southwardslopes, the individual solar cells are attached so that the longitudinaldirection of the grooves 8 crosses the direction of inclination of theroof at right angles as shown in FIG. 4. This style of attachment cansuccessfully limit the irradiation status causative of a large shadowingloss within the time zone around the meridian passage so as to minimizethe influences by the shadowing loss possibly occurs, and on thecontrary, can effectively convert sunlight, which is irradiated from theeast in the morning or from the west in the evening, into electric powerwhile successfully suppressing the shadowing loss.

[0047] In this case, the solar cells 14 are consequently installed so asto horizontally align the longitudinal direction of the grooves 8.Taking the angle of inclination β of the light-receiving surface and thelatitude δ of the installation site into consideration, the inventorsextensively investigated into optimum direction of the electrode andfound it advantageous to adopt a mode of installation as describedbelow. That is, assuming now that the angle of inclination of thelight-receiving surface away from the horizontal plane as β°, and thatthe latitude of the installation site as δ° (where, the north latitudeside is defined as positive), it is defined that the solar cell moduleis installed so as to direct the electrode-forming inner side faces ofthe grooves more closer to the equator than the other inner side faces(that is, so as to direct it upward in the direction of inclination) asshown in FIG. 5 when the relation of

β≦60×|sin δ|  (1)

[0048] is satisfied, and vice versa as shown in FIG. 6 when the relationof

δ>60×|sin δ|  (2)

[0049] is satisfied.

[0050] That is, at a latitude δ where the relation (1) holds, adoptionof the installation mode shown in FIG. 5 can raise the annual poweroutput as compared with that attainable by the installation mode shownin FIG. 6, and at latitude δ where the relation (2) holds, adoption ofthe installation mode shown in FIG. 6 can raise the annual power outputas compared with that attainable by the installation mode shown in FIG.5. The annual power output of the solar cell module 60 can be thusoptimized. FIG. 10 shows a graph expressing the conditional relations(1) and (2) in the above. The south latitude side is defined as negativein FIG. 10.

[0051] The relations (1) and (2) were derived according to the thinkingflow shown in FIG. 9. The following paragraphs will detail the processof thinking. First, as shown in FIG. 2, expressions for describing ratioof projected area of the electrode 5 (shadowing loss) are found based onazimuth and elevation angle of the sun, and angle of installation andazimuth of the solar cell module 60. As is clear from FIG. 2,

B/(A+B+C) and B′/(A′+B′+C′)  (3)

[0052] represent the ratio of projected area of the electrode 5. Asshown in step S1 in FIG. 9, the azimuth φ′ and elevation angle θ′ of thesun (where, azimuth φ′ is defined while assuming the east aspect in thelongitudinal direction of the grooves as 0, and the direction ofcounter-clock-wise rotation as positive) are expressed as a function ofdate d, time of day hr and latitude δ. Data for the function canprimarily be determined according to calendar. Methods of dataacquisition are publicly known in the field of astronomy, and will notbe detailed here. Then as shown in step S2, the aforementioned azimuthφ′ and elevation angle θ′ are processed by rotational conversion as muchas the angle of inclination η of the light-receiving surface (alsoreferred to as installation angle of the solar cell module, or moresimply as installation angle), to thereby determine function data whichexpresses relative azimuth φ and elevation angle θ of the sun as viewedfrom the light-receiving surface (solar cell module). The elevationangle θ corresponds to the angle of incidence of sunlight on thelight-receiving surfaces, and the azimuth φ corresponds to an anglebetween the groove 8 and the positive solar projection, so that assumingthat all of the thickness (t) of the electrode, depth (h) of the groove,width (w2) of the groove and distance (w1) between the grooves are givenas constant parameters as shown in FIG. 19, shadowing loss (S) for eachdate/hour can be calculated based on the above expressions (3) asfunctional data of latitude δ and installation angle β by using theaforementioned θ, φ, and shape parameters of the groove (step S3 in FIG.9).

[0053] The relative azimuth φ and elevation angle θ of the sun as viewedfrom the light-receiving surface can be calculated as described below(although the following description will be made referring to theregions in the northern hemisphere, outline of the calculation is, ofcourse, identical also for the southern hemisphere). First, a positionof the sun as viewed from the equator at a given time hr of day isdetermined. For this purpose, a celestial sphere having a diameter of 1is assumed as shown in FIG. 23, where the east falls in the positive xdirection, the north falls in the positive y direction, and the uppervertical direction falls in the positive z direction. In this case,position (x, y, z) of the sun on the celestial sphere can be determinedbased on three following equations (4) through (6), where time of themeridian passage of the sun is defined as hr=12: $\begin{matrix}{x = {\sqrt{1 - y^{2}}{\cos \left( {\frac{\pi}{12}\left( {{hr} - 6} \right)} \right)}}} & (4)\end{matrix}$

 y=−cos(α)  (5) $\begin{matrix}{z = {\sqrt{1 - y^{2}}{\sin \left( {\frac{\pi}{12}\left( {{hr} - 6} \right)} \right)}}} & (6)\end{matrix}$

[0054] In the above equation, α represents angle of meridian passage onthe dth day from January 1 (January 1 is the 1st day), and is given bythe equation (7) below: $\begin{matrix}{\alpha = {{90 \times \frac{\pi}{180}} + {23.45 \times \frac{\pi}{180}{\sin \left( {\frac{360}{365}\left( {d - 81} \right) \times \frac{\pi}{180}} \right)}}}} & (7)\end{matrix}$

[0055] It is noted now that the orthogonal coordinate (x, y, z) and thepolar coordinate in the celestial sphere (R, φ′, θ′) are in geometricalrelations of x=cos θ′×cos φ′, y=cos θ×sin φ′ and z=sin θ′. Next, aposition of the sun (x1, y1, z1) as viewed from a point of land at δ°latitude is determined. A position of the sun as viewed from a point ofland at δ latitude equals to a position obtained by rotating theposition of the sun as viewed from the equator around x axis (east-westdirection) by δ°, and is given by three following equations (8) through(10):

x1=x  (8)

y1=y cos(δ)−z sin(δ)  (9)

z1=y sin(δ)+z cos(δ)  (10)

[0056] Next, a position of the sun (x2, y2, z2) as viewed from themodule installed so as to face a direction ψ° off-angled from due southis determined, where sign of ψ is given while assuming the eastdirection as positive. The position of the sun in this case equals to aposition obtained by rotating the position of the sun (x1, y1, z1)around z axis by ψ°, and is given by three following equations (11)through (13):

x2=x1 cos(ψ)−y1 sin(ψ)  (11)

y2=x1 sin(ψ)+y1 cos(ψ)  (12)

z2=z₁  (13)

[0057] A position of the sun (x3, y3, z3) as viewed from the solar cellmodule is further determined. It is assumed now, as shown in FIG. 24,that the solar cell module herein is installed so as to align thelongitudinal direction of the grooves in parallel to the horizontalplane and at an installation angle of β°. It is also noted that thelongitudinal direction of the grooves is defined as x′ direction, thedirection normal to the longitudinal direction of the grooves and inparallel to the light-receiving surface as y′ direction, and thedirection of the normal line on the module as z′ direction. Also in thiscase, a position of the sun as viewed from the solar cell module equalsto a position obtained by rotating the position of the sun around x′axis by −β°, and is given by three following equations (14) through(16):

x3=x2  (14)

y3=y2 cos(−β)−z ₂ sin(−β)  (15)

z3=y2 sin(−β)+z2 cos(−β)  (16)

[0058] Therefore the azimuth φ and elevation angle θ of the sun asviewed from the solar cell module can be expressed by equations (17) and(18) below using the position of the sun (x3, y3, z3): $\begin{matrix}{\varphi = {\tan^{- 1}\left( \frac{y3}{x3} \right)}} & (17) \\{\theta = {\tan^{- 1}\left( \frac{z3}{\sqrt{{x3}^{2} + {y3}^{2}}} \right)}} & (18)\end{matrix}$

[0059] where, the azimuth φ is defined while assuming the east aspect inthe longitudinal direction of the grooves as 0, and the direction ofcounter-clock-wise rotation as positive. The elevation angle θ isdefined as positive when the sunlight can directly be incident to thelight-receiving surface of the solar cell module. As a consequence, theazimuth φ and elevation angle θ of the sun as viewed from the solar cellmodule can be calculated by providing the aforementioned equations (4)through (18) with five variables of latitude δ of the installation siteof the module, installation angle β, installation azimuth ψ, date d, andtime of day hr.

[0060] Next, according to the above-described principle, calculationsare made on the shadowing loss S on various date/hour throughout an yearfor both cases where the electrode-forming inner side faces 1 aredirected upward and downward, while varying the latitude δ andinstallation angle β. In the best mode for carrying out the invention,representative data points were collected by observing the shadowingloss S for each time of day on 15th day of every month, which is amid-month representative day, while fixing the installation azimuth ψ to0, varying the latitude δ at 10° intervals, and also varying theinstallation angle at 5° intervals. FIGS. 11, 12 and 13 show calculatedresults of the shadowing loss S measured at 8 a.m., 10 a.m., 12 noon, 14p.m. and 16 p.m. on the 15th day of every month for the cases where thesolar cell module is situated at 30° latitude and at installation anglesβ of 25°, 30° and 35°, respectively. FIGS. 14, 15 and 16 show calculatedresults of the shadowing loss S measured at 8 a.m., 10 a.m., 12 noon, 14p.m. and 16 p.m. on the 15th day of every month for the cases where thesolar cell module is situated at 50° latitude and at installation anglesβ of 45°, 50° and 55°, respectively.

[0061] Referring now back to FIG. 9, calculation is made in step S4 todetermine effective amount of received solar energy Pe after beingsubtracted by the shadowing loss S. It was assumed herein that solarenergy density on the surface normal to the sunlight was presumed as 1kW/m² as an average irrespective of the latitude, time of day andelevation angle of the sun. Note that only a component incident alongthe direction of the normal line on the module can contribute the solarenergy density irradiated on the module. It was also assumed that onlyscattered light could reach the light-receiving surface for the casewhere the sunlight could not directly irradiate the module during thedaytime (i.e., from sunrise to sunset), where the solar energy densitywas assumed constantly at 0.3 kW/m² irrespective of the angle ofincidence. That is, the effective amount of received solar energy isgiven by a value obtained after subtracting the shadowing loss from 0.3kW/m² irrespective of location of the sun. This is typified by a casewhere the sun comes behind the module 60 depending on the seasons andtime zones, as shown in FIG. 7. Effective amount of received solarenergy during the nighttime (from sunset to sunrise) was assumed as 0kW/m².

[0062] Next, in step S5, the effective amount of received solar energyPe thus calculated based on the aforementioned assumptions arecumulatively counted for all time of day and then divided by all time ofday, to thereby obtain average effective amount of received solar energyPea. Relations between the average effective amount of received solarenergy Pea and installation angle β are shown in FIG. 17 (latitude δ=30°) and FIG. 18 (latitude δ =50°). As is obvious from these graphs,superiority-inferiority relation between the cases where theelectrode-forming inner side faces are directed upward and downwardinverts at a certain turning point, where the upward placement isadvantageous in the smaller angle region, and the downward placement isadvantageous in the larger angle region. It is also found that theturning point where the inversion in the superiority-inferiorityrelation occurs varies depending on the latitude δ. For example, thecase of latitude 30° shows an angle of turning point of approx. 30°.This means that the electrode-forming inner side faces are preferablydirected downward (direction of the equator) when P is larger than theangle of turning point, and directed upward (direction opposite to theequator) when β is smaller than the angle of turning point. On the otherhand, the case of latitude 50° shows an angle of turning point ofapprox. 47°.

[0063] Referring now back to FIG. 9, calculation is then made in step S7to determine the angle of turning point for the individual latitudes δ.FIG. 10 is a graph obtained by plotting results of the calculationagainst latitude δ. It is found from the graph that the plot falls tozero at latitude 0° (equatorial position), which indicates that nosuperiority-inferiority relation is found between the upward placementand downward placement, and that the angle of turning point increasesaccording to a sine curve as δ shifts towards the northern latitude sideor towards the southern latitude side. These relations correspond to theaforementioned conditional discriminant (1) and (2). While the groovemorphology of the OECO solar cell used in the calculation has a width(w1) of the projected portion 9 of 50 μm, a width (w2) of the groove of450 μm, a depth (h) of the groove of 50 μm, and a thickness (t) of theelectrode of 5 μm as shown in FIG. 19, substitution of any differentvalues will finally give similar curves. It is to be noted that bus barelectrodes were ignored in the derivation, because the shadowing loss ofthe bus bar electrodes do not vary with the angle of incidence.

[0064] In the invention, total amount of annual power output obtainablefrom the solar cell module 60 can be increased by determining theinstallation direction of the electrode-forming inner side faces of thesolar cell module 60 based on these discriminants, and by installing themodule according thereto. It is to be noted that the discriminants ofthe invention are applicable from 90° North Latitude to 90° SouthLatitude.

[0065] It may not always be possible to ensure best position having asouth aspect for installing the solar cell module 60, as shown in FIG.20. FIG. 20 shows a case where the module must unwillingly be installedon a roof having an east aspect (having an eastward and westwardslopes). In this case, the installation azimuth ψ is not equal to zero.It is therefore preferable to attach the solar cells to the support(cell holding member 10 herein) so as to direct the longitudinaldirection of the grooves 8 (i.e., electrode-forming inner side faces)normal to the north-south direction (in parallel to the east-westdirection). In this case, direction of the slopes of the light-receivingsurfaces also lie in the east-west direction.

[0066]FIG. 25 shows calculated results of the installation angle β atvarious latitudes δ when the installation azimuth ψ is not equal tozero. It is found from the graph that no distinctive changes inrelations between the installation angle β and latitude δ are observedup to an installation azimuth ψ of 65°, indicating that there will be noproblem if the aforementioned discriminants (1) and (2) are appliedwithout any modification. On the other hand, an installation azimuth ψexceeding 65° (90° at maximum) results in considerable increase indeflection of the curves from the sine curves expressed by the righthand sides of the discriminants (1) and (2), indicating inadequacy ofthese discriminants as those for discriminating direction of thegrooves. To cope with the cases with installation azimuth ψ exceeding65°, the inventors then conducted curve-fitting study so as to fit afunction to the points expressing the calculated results of installationangle β for various latitudes δ, and found it effective to use thediscriminants below. That is, the solar cell module is preferablyinstalled so as to direct the electrode-forming inner side faces of thegrooves more closer to the equator than the other inner side faces whenrelation (19) below is satisfied, and vice versa when relation (20)below is satisfied. It is to be noted that, for the case where ψ is 90°(the module having an east aspect), the solar cell module is installedso as to direct the electrode-forming inner side faces of the groovesmore closer to the east or downward than the other inner side faces whenrelation (19) below is satisfied, and vice versa when relation (20)below is satisfied. On the other hand, for the case where ψ is −90° (themodule having a west aspect), the solar cell module is installed so asto direct the electrode-forming inner side faces of the grooves morecloser to the west or downward than the other inner side faces whenrelation (19) below is satisfied, and vice versa when relation (20)below is satisfied. $\begin{matrix}{\beta \leq {{{- 32.5} \times {\cos \left( {2 \times \left( {\delta + {{\omega \left( {1 - \frac{\delta}{90}} \right)} \times {\sin \left( {2 \times \delta} \right)}}} \right)} \right)}} + 32.5}} & (19) \\{\beta > {{{- 32.5} \times {\cos \left( {2 \times \left( {\delta + {{\omega \left( {1 - \frac{\delta}{90}} \right)} \times {\sin \left( {2 \times \delta} \right)}}} \right)} \right)}} + 32.5}} & (20)\end{matrix}$

[0067] where, ω=−0.0043δ³+0.9δ²−62.5δ+1461.

[0068] As is obvious from FIG. 10, regions having higher latitudes havelarger angles of turning point regarding the upward and downwardorientation of the electrode-forming inner side faces. This is becausethe higher-latitude regions have only small angles of incidence ofsunlight throughout an year, and larger angles of inclination of thelight-receiving surface take larger advantages. As has been described inthe above, there may be the case where the angle of inclination δ per sehas an optimum value depending on latitude δ of the installation site.It is therefore allowable to configure the solar cell module of theinvention so as to make the angle of inclination δ of thelight-receiving surface variable as shown in FIG. 22. In the best modefor carrying out the invention shown in FIG. 22, the lower end portionof the cell holding member 10 is joined through a hinge 53 with a base150 in a swinging manner so that the angle of inclination β can bevaried by ascending or descending the upper end of the cell holdingmember 10 using an elevation rod 54.

[0069] The elevation rod 54 is typically configured as being integratedwith a female screw 54 a, where the female screw 54 a is engaged with ascrew axis 55, and the elevation rod 54 can be ascended or descended byrotating the screw axis 55 in the forward or reverse direction typicallythrough operation of a handle 56.

EXAMPLE 1

[0070] The solar cell shown in FIG. 1 was fabricated by the methoddescribed below. First, on the light-receiving surface side of thep-type, single crystal silicon wafer 2 containing gallium, a Group IIIelement, as an impurity (10 cm square, 300 μm thick, specific resistance0.5 Ω·cm), a plurality of parallel grooves 8 having a square(rectangular) section were formed using a dicer. The groove morphologywas defined, as shown in FIG. 19, by a distance (w1) between the groovesof 50 μm, a width (w2) of the groove of 450 μm, and a depth (h) of thegroove of 50 μm. Damaged layer produced in the wafer was then removed byetching using an aqueous potassium hydroxide solution, and the siliconnitride film 6 was formed on the back surface using a plasma-assistedCVD apparatus.

[0071] The emitter layer 3 comprising an n+-type region was then formedon the light-receiving surface side of the silicon wafer 2 by thermallydiffusing phosphorus, which is a Group V element, so as to adjust thesheet resistance to 100 Ω/□. On the back surface of the silicon wafer 2,the electrode 7 of 2 μm thick was formed by depositing aluminum byvacuum evaporation. Next, the tunnel oxide film 4 of 2 nm thick wasformed on the light-receiving surface by thermal oxidation, and aluminumfor forming the electrodes was succeedingly deposited by vacuumevaporation from a direction normal to the longitudinal direction of theparallel grooves and inclined 20° away from the surface of the wafer, tothereby form the electrode 5 of 5 μm thick only on one side face of eachgroove. Further thereon, the silicon nitride film 6 of 70 nm thick wasformed over the entire surface of the light-receiving surface byplasma-assisted CVD.

[0072] Sixty similarly-fabricated OECO solar cells were then attached tothe support composed of glass and Tedlar so that the electrode-forminginner side faces 1 are arranged on the same side, and so that thelongitudinal directions of the grooves coincide with the bottom edge ofthe solar cell module, and molded with EVA (ethylene-vinyl acetate)resin into the solar cell module. A comparative solar cell module wasalso fabricated in which half of the solar cells were attached so thatthe electrode-forming inner side faces 1 are inverted by 180°. Theformer is referred to as Sample 1, and the latter as Sample 2 forconvenience. Module area of thus fabricated solar cell modules was 666cm², and rated output of the samples was 110 W.

[0073] Output characteristics of thus-fabricated solar cell modules weremeasured using a solar simulator (light intensity: 1 kW/m², spectrum:AM1.5 global). In the measurement, the light-receiving surfaces of thesolar cell modules were inclined 60° away from the direction normal tothe grooves. Obtained output characteristics were listed in Table 1.TABLE 1 Short-circuit Open-circuit Fill factor Maximum current (A)voltage (V) (%) output (W) Sample 1 7.0 17.6 77.1 95.3 Sample 2 6.5 17.577.2 88.6

[0074] From the measurement results, Sample 1 was found to showshort-circuit current larger by approx. 0.5 A than that of Sample 2,indicating a larger output. It is therefore to be understood that higheroutput is obtainable by adopting the invention.

EXAMPLE 2

[0075] As judged from the discriminants (1) and (2) of the invention,the installation at 30° North Latitude and at an installation angle of35° can yield optimum results when the electrode-forming inner sidefaces are directed downward. For a demonstration purpose, the inventorsinstalled the solar cell module fabricated in Example 1, in which allelectrode-forming inner side faces 1 are unidirectionally aligned, on aroof having a slope inclined 35° away from due south in Yaku Island,Kagoshima Prefecture, Japan situated at 30°20″ North Latitude, and theannual power output was measured. Samples used herein were one solarcell module having electrode-forming inner side faces directed upwardand one solar cell module having those directed downward. Measurementresults of the annual power output were listed in Table 2. TABLE 2Module having Module having electrode- electrode-forming inner forminginner side face side face directed directed downward upward Annual power118.7 117.9 output (kWh)

[0076] From the measurement results, the solar cell module installed soas to direct the light-receiving inner side faces downward showed alarger annual power output than that of the solar cell module installedupward.

1. A solar cell module comprising: a plurality of solar cells having aplurality of parallel grooves on the individual light-receiving surfacesthereof, each of the grooves having an electrode for extracting outputon the inner side face (referred to as electrode-forming inner sideface, hereinafter) on one side in the width-wise direction thereof; anda support for supporting the solar cells in an integrated manner so asto direct the light-receiving surfaces upward; wherein the plurality ofsolar cells are attached to the support so that the longitudinaldirections of the grooves nearly coincide with each other, and so thatthe electrode-forming inner side faces are arranged on the same side. 2.The solar cell module as claimed in claim 1, wherein the plurality ofsolar cells are attached to the support so that positions of theelectrode-forming inner side faces are arbitrarily selected between afirst position and a second position which are in a 180°-invertedpositional relation within a plane parallel to the light-receivingsurface.
 3. The solar cell module as claimed in claim 2, wherein theplurality of solar cells are collectively attached to a cell holdingmember, the cell holding member being attached to an installation baseas the support, and being configured so that variation in the angle ofattachment of the cell holding member to the installation base canresult in positional changes in the electrode-forming inner side facesof the plurality of solar cells collectively between the first positionand the second position.
 4. The solar cell module as claimed in any oneof claims 1 to 3, wherein the grooves have any section of rectangular,semicircular and triangular forms.
 5. A method of installing the solarcell module as claimed in any one of claims 1 to 4 at a predeterminedinstallation site, wherein the direction of arrangement of theelectrode-forming inner side faces of the grooves of the individualsolar cells are adjusted depending on the angle of inclination δ of thelight-receiving surfaces of the as-installed individual solar cells awayfrom the horizontal plane, and on the latitude δ of the installationsite of the solar cell module.
 6. The method of installing the solarcell module as claimed in claim 5, wherein the solar cell module isinstalled so as to horizontally align the longitudinal direction of thegrooves formed on the individual solar cells, and assuming that theangle of inclination of the light-receiving surface away from thehorizontal plane as β°, and that the latitude of the installation siteas δ° (where, the north latitude side is defined as positive), the solarcell module is also installed so as to direct the electrode-forminginner side faces of the grooves more closer to the equator than theother inner side faces when the relation of β≦60×|sin δ| is satisfied,and vice versa when the relation of β>60×|sin δ| is satisfied.